<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<script>
    console.log(typeof "hello");//console.log()控制台输出内容
    console.log(typeof 222);//"number"
    console.log(typeof '222');//"string"
    console.log(typeof false);
    console.log(typeof "false");//这个上面的都是基本数据类型/
    console.log(typeof null);//object//object function 是引用数据类型；
    console.log(typeof {});
    console.log(typeof function () {});//function

    //变量是数据的代言人；
    var demoStr="hello";
    console.log("-----------------------");
    console.log(typeof demoStr);//string
    demoStr=22;//不推荐这么做 ；
    console.log(typeof demoStr);//number

    //typeof 总是返回string类型的； typeof()
    console.time("123");
    console.log("+++++++++++++++++++++");
    console.log(typeof (typeof "hello"));
    console.log(typeof (typeof 222));
    console.log(typeof typeof '222');
    console.log(typeof typeof false);
    console.log(typeof typeof "false");
    console.log(typeof typeof null);
    console.log(typeof typeof {});
    console.log(typeof typeof function () {});
    console.timeEnd("123");

    console.assert(1==1,"打脸了");

    var aloneVal=Symbol();
    console.log(typeof aloneVal);//symbol  存在的意义，避免多人开发时，变量覆盖；

</script>
</body>
</html>